51P/Harrington (0051P)


Type: Periodic Perihelion date: 5 October 2022 Perihelion distance (q): 1.7 Aphelion distance (Q) : 5.7 Period (years): 7.1 Eccentricity (e): 0.54 Inclination (i): 5.4 JPL orbit diagram COBS lightcurve Robert G. Harrington discovered this comet on a plate taken on 14 August 1953 with the 122-cm Schmidt camera during the National Geographic Society-Palomar Sky Survey. The comet was in Aquarius. He estimated the magnitude as 15, and described the comet as diffuse, with a central condensation, and a tail less than 1° long. This was a very favourable apparition for this comet, with its perihelion and closest approach to Earth coming within 10 days of one another during September 1953. The comet's brightness held near 15 throughout September and then began fading. The magnitude had dropped to 18 during the final days of October, and was determined as 18.8 when last seen on 10 December. During 1967, Grzegorz Sitarski (Institute of Astronomy, Polish Academy of Sciences, Warsaw, Poland) computed corrected orbital elements for the 1953 apparition. He then advanced the comet backwards to check on its recent orbital evolution. Sitarski noted the comet's orbital period was 6.65 years when it passed perihelion in 1918. It then passed 0.8 AU from Jupiter on 19 November 1920 and the orbital period was changed to 6.99 years. The result of this nearly 7-year orbital period was that the apparitions of 1925, 1932, 1939, 1946, and 1953 were all nearly identical, having passed perihelion within a few days of 25 September each time. These favourable conditions ended because of a close approach to Jupiter on 26 October 1956 (0.50 AU). Sitarski noted that the 1953 apparition "was the last opportunity to discover this faint comet on the sky." B. G. Marsden investigated the orbit of this comet and predicted it would next arrive at perihelion on 28 June 1960. Elizabeth Roemer (U. S. Naval Observatory, Flagstaff station, Arizona, USA) recovered this comet on 3 August 1960. The magnitude was estimated as 19, and the comet was described as diffuse, with a condensation, and a tail less than 1° long. The comet changed little in brightness from its recovery until it was last seen on 26 October when Roemer determined the magnitude as 19.8. This was primarily because the comet was steadily approaching Earth, the closest distance being 1.13 AU on November 4. The comet was not observed during its returns in 1967 and 1974 since perihelion occurred when the comet was in conjunction with the sun. The comet was next recovered on 4 September 1980 when P. Jekabsons photographed it at magnitude 18.5. This was still not a favourable apparition and the comet was not seen after 6 October. It was also seen during its returns in 1987 and 1994. The latter was very favourable, allowing amateur astronomers to make observations as it reached magnitude 13.5. This comet surprised astronomers during its 1994 return. IAU Circular 6089, reported that Jim Scotti (Lunar and Planetary Laboratory, Arizona, USA) discovered two companions on 5 October 1994. The magnitude of the primary was 12.8, while the two fragments shown at 21.3 and 20.2. Following the 2001 apparition it approached to within 0.37 AU of Jupiter on 23 October 2003, which rotated the orbit's ascending node by over 30 degrees and increased the perihelion distance from 1.568 AU to 1.688 AU. The orbital period changed from 6.77 to 7.13 years. Overall this will make the comet an even fainter object at each perihelion passage. The next close approach will not occur until 2039 (0.41 AU). Observations (VEMag = visual equivalent magnitude) Date 10x10 mag Error VEmag Coma ' 24-Aug-15 19.49 0.10 16.9 0.2 07-Sep-15 19.25 0.12 16.7 0.2 14-Sep-15 19.31 0.32 18.7 0.2 08-Oct-15 18.72 0.02 16.9 0.2 20-Oct-15 18.75 0.04 17.6 0.2